1985 Volkswagen Quantum Base, AutomaticFACTORY OEM SERVICE PROCEDURE

Altitude Sensor

NOTE: Testing altitude sensor should be done if differential pressure regulator current readings are incorrect based upon altitude.
  1. Connect test harness between differential pressure regulator and vehicle harness. Connect multimeter to test harness. Disconnect wiring from coolant temperature sensor and leave unplugged. Replace fuel pump relay with Jumper Switch (US 4480/3) in off position.
  2. Disconnect wiring from altitude sensor. Activate fuel pump and turn on ignition. Differential pressure regulator current reading should be 8-12 mA. Bridge terminals 1 (signal) and 2 (+/power) of altitude sensor connector with jumper wire. Differential pressure regulator current reading should be 11-14 mA.
  3. Bridge terminals 1 and 3 (-/ground) of altitude sensor connector. Differential pressure regulator current reading should be 0-4 mA. If readings are correct, replace altitude sensor and reset CO. If readings are incorrect, check for open circuit between altitude sensor and ECU. If wiring is good, replace ECU.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.